Within biology there is a branch called cell biology, previously known as cytology, which is responsible for the study of cells. These microorganisms that make up all living things have their own characteristics and structures, depending on the type they are. As they are a very broad and complex subject, we are going to focus today on a more botanical part: the plant cell wall.
If you are interested in the subject and want to know more about this small part of plant cells, I recommend that you continue reading. We will explain what the function of a plant cell is before saying what the plant cell wall is. Then we will talk about its structure and its components.
What is the function of the plant cell?
Before talking about the plant cell wall, let’s first clarify the function of plant cells. They are a type of eukaryotic cell that form plant tissues in those organisms that are part of the kingdom Plant.
They have certain similarities with the cells of animals. In both cases, they are eukaryotic cells that contain a differentiated nucleus, cytoplasm, membrane, and hereditary genetic information. also known as DNA. However, there is a very important difference between the two types of cells. Vegetables have the ability to photosynthesize. It is a chemical process by which plants use light energy to synthesize organic substances, thus releasing oxygen.
What is the plant cell wall?
When we talk about the plant cell wall, we mean a rigid and resistant layer that supports various osmotic forces and growth. Its location is the outside of the plasma membrane in the cells of plants, as well as fungi, bacteria, archaea and algae. The function of the wall is protect cell content, give rigidity and define the structure of plants. In addition, it acts as a mediator between the cell and the environment.
What is the structure of the plant cell wall?
The plant cell wall has a total of three fundamental parts in terms of its structure. We are going to comment on them below:
- Primary wall
It is usually between 100 and 200 nanometers thick and is found in all plant cells. It is a wall composed of an accumulation of three or four layers of cellulose microfibrils. It is perfectly adapted to cell growth thanks to the microfibrils, as these slide between them, producing a longitudinal separation.
- Secondary wall
Although it is very common, it does not exist in all plants. The secondary wall is a layer adjacent to the plasma membrane. Contains a lot of cellulose, lignin and suberin. In addition, it is not deformable nor does it allow cells to grow. Once cell growth has come to an end, the secondary wall is formed. Generally, it is much thicker than the primary wall in woody tissues.
- Middle lamella
The middle lamella is a layer whose function is to join the primary walls. Its main components are pectin and hemicellulose.
Composition of the plant cell wall
Regarding the composition of the plant cell wall, it varies according to the type of cell and the different taxonomic groups. Usually, It is made up of a network made of carbohydrates, proteins, and phospholipids. All of them are embedded in a gelatinous matrix that in turn is composed of other proteins and carbohydrates.
Cellulose is the main component of the plant cell wall. It is a fibrillar polysaccharide that is organized into microfibrils. Between 15% and 30% of the dry weight of plant cell walls correspond to this organic biomolecule. Regarding cellulose microfibrils, these are bound by non-fibrillar carbohydrates, called hemicellulose.
What is chlorophyll
There is another very important component for the plant cell wall: Pectin. This non-fibrillar polysaccharide is rich in highly hydrated D-galacturonic acid and its branching is heterogeneous. The pectin matrix is responsible for the porosity of the wall. In addition, it provides fillers whose function is to regulate the pH.
Another component of the plant cell wall are structural proteins. These are usually rich in one or two amino acids, they are glycosylated and have domains with repeating sequences. Most of these proteins have a fibrillar structure that is immobilized through a covalent bond between them or with carbohydrates. Today we know that structural proteins accumulate in the plant cell wall during different stages of development and also in response to various stressful conditions. These are the structural proteins of the plant cell wall:
- HRGPs: Hydroxyproline-rich proteins, extensins
- PRP’s: Proline-rich proteins
- GRP’s: Glycine-rich proteins
- AGP’s: Proteins rich in arabinogalactans
Within the network of proteins and polysaccharides, there are also several soluble proteins:
- Enzymes that are related to the manufacture of nutrients, such as glucosidase.
- Enzymes that are related to wall metabolism. Example: Xyloglucanotransferases, peroxidases, laccases
- Defense-related proteins
- Transport proteins
There are also other polymers that are part of the composition of the plant cell wall. After cellulose, the most abundant component is lignin. It is a rigid amorphous polymer that is the result of the union of phenylpropyl alcohols and various acids. It normally accumulates on secondary walls. However, they may occasionally appear in the middle lamella of dead or necrotic tissue.
Cutin and suberin are other plant cell wall polymers. These are made of long-chain fatty acids whose binding to each other creates a rigid, three-dimensional network. Both polymers usually accumulate on secondary walls, but they can also appear on primary walls in an exceptional way.
Waxes remain to be highlighted. These do not provide rigidity, but yes, impermeability to water. Cutin and suberin also provide a bit of waterproofing, but not as much.
In biology in general, cells are a whole world that is still being investigated today. We have only talked about part of plant cells here, but there is much more to learn.